This invention relates to method and means for mooring a tethered balloon and, more particularly, the invention is concerned with providing a four rope equilateral square pyramid arrangement attached to the nose of a balloon for mooring the balloon without the necessity of a mooring mast and accompanying massive nose structure.
Tethered aeroform balloons can be moored by brute force methods and by weathervane or windward systems. Brute force mooring is accomplished by tying the balloon to the ground, immobile, and may be performed by ropes, nets or use of a large pit. These techniques are unsatisfactory primarily because of the excessive danger of damage to the balloon and because of the danger of injury in high wind conditions. Of the weathervane systems, the use of a gondola which is detachable for flight is one method although not applicable to the present invention as will be understood later. Another system presently in use is the monorail and it will be considered in detail below. Both of these last-named systems as well as any other weathervane system use a tower or mast to which the balloon is attached. Of these two systems the gondola method has a significant disadvantage, namely, that is does not mechanically anchor the balloon to the ground, this function being performed only by the tower attachment. This attachment point is neither strong enough nor correctly placed to resist the forces induced by gusty strong winds. Another problem with the gondola mooring system is that it must be attended, that is, a watchman is required to add or remove ballast to ensure that the balloon remains horizontal as temperature variations change the net lift or buoyancy due to gas expansion.
Now considering the monorail system, the balloon being buoyant exerts a relatively large upward pull on the dolly and on the masthead. The force is greater than the payload capacity, the weight of the tether cable, plus the free-lift margin. An upward force of several thousand pounds is commonplace and is distributed between the confluence point and the masthead. The balloon is ordinarily flown at a positive pitch angle of 10.degree. to 15.degree. for aerodynamic reasons. This angle is established by the distance forward or back the confluence point is rigged for a given weight and balance configuration. It would be desirable to reduce the upload on the mast to some very low value but this would obviously require re-rigging the balloon for mooring by moving the confluence point forward which is operationally inconvenient. Another way of reducing mast tension is to hang ballast on the nose which is both inconvenient and structurally undesirable. In a typical monorail mooring system the mast height is about 39 feet, eight steel guy cables are used at an interior base angle of about 60.degree. and the added nose structure on the balloon weighs about 600 pounds. The mast, the guys and the circular monorail are fixed to the ground with ground-anchors and/or poured concrete piers.
Although the nose structure is used only for mooring, it is carried by the balloon in flight. It is thus a functionally unnecessary flight component which adversely affects the balloons altitude and payload capability. It is also expensive and very time consuming to install. Consequently, it would be most desirable to dispense entirely with the nose structure and while so doing, it would also be desirable to eliminate the necessity of providing a mast tower. The sole function of the nose structure is to protect the nose of the balloon from damage by the tower. A proposed solution to the problem was to position a large cup on the tower. Although the principal disadvantage is thus avoided, it neither is simple, inexpensive nor convenient. In order to eliminate the nose structure, it is first necessary to eliminate the mast.
Under conditions of no wind, the tower operates in tension only and, in fact, the guys are unnecessary. The tower restrains the balloon from assuming its normal 10.degree.-15.degree. nose-up attitude. Usually the wind is blowing and the balloon pivots around the tower so as to head upwind. The latch rotates and the dolly rides around the monorail as the balloon responds to the wind azimuth. If the wind is steady in direction and speed, the side forces on the tower are small. In gusty winds however, the drag load of the balloon can impose suprisingly large loads on the tower. A sudden reduction in velocity, for example, will cause the balloon to spring-back and ram the tower. Also, a sudden change in the wind azimuth will put a large side load on the tower. The response time of balloon is long because of its high inertia and during the time it is righting itself, the reaction on the tower is large. Obviously, one reason that the side force is so large is that the tower is rigid and fixed. Thus, it would be most desirable to provide a structural arrangement which would restrain the steady-state upward force while at the same time permitting moderate but limited lateral movement of the nose. By allowing this small lateral freedom, little of the high reaction force would develop, yet the long term azimuth pivot requirement would be met.